As the use of cellular phones has increased, the likelihood of signal interference has also increased. One cause of signal interference is intermodulation distortion (IMD), such as passive intermodulation (PIM). A PIM is an unwanted signal or signals generated by the non-linear mixing of two or more frequencies in a passive device such as a connector or cable. PIM has surfaced as a problem for cellular telephone technologies such as Global System for Mobile Communications (GSM), Advanced Wireless Service (AWS), Personal Communication Service (PCS) systems, Code Division Multiple Access (CDMA), Universal Mobile Telecommunication System (UMTS), and Long Term Evolution (LTE). Cable assemblies connecting a base station to an antenna on a tower using these cellular systems typically have multiple connectors that cause PIMs that can interfere with system operation. For example, when PIM signals are generated, they can cause interference on the signals at neighboring frequencies, and even other signals out of band. Typically, PIM degrades performance, increases call drop rates and decreases cell coverage.
The PIM signals are created when two signals from the same or different systems mix at a PIM point such as a faulty cable connector. If the generated PIM harmonic frequency components fall within the receive band of a base station, it can effectively block a channel and make the base station receiver think that a carrier is present when one is not. PIMs can, thus, occur when two base stations operating at different frequencies, such as an AWS device and a PCS device, are in close proximity. PIM can also occur when one base station operates according to two or more technologies such as GSM and UMTS or at multiple carrier frequencies.
However, conventional PIM test equipment is relatively expensive and heavy.